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Reinforced Autoclaved Aerated Concrete

Concerns regarding the structural integrity of RAAC have been evident for a number of years, although only recently (September 2023) have these concerns been widely reported in the public domain, as an increasing number of structural failures involving RAAC have been identified promoting Government intervention.



Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight cementitious material. It is aerated and has no coarse aggregate, meaning the material properties and structural behaviour differ significantly from ‘traditional’ reinforced concrete. RAAC has been used in building structures in the UK and Europe since the late-1950’s and up to the mid-1990’s, most commonly as precast roof panels or planks in flat roof construction but occasionally in pitched roofs, floors and wall panels in both loadbearing and non-loadbearing arrangements. There is also evidence that it has been used in a limited number of buildings through the 1990’s and 2000’s.

RAAC was used in a range of building types, both public and private sector, but is believed to be more common in schools, hospitals and public buildings. It has been discovered in courts, theatres, sports halls, , and a range of non-domestic buildings. It’s use in residential buildings is thought to be limited to roof top plant rooms, and some wall panels. Certain product names such as Siporex, Durox, Celcon, Hebel and Ytong are indicators of RAAC. 

RAAC has proven to be not as durable as other concrete building materials. It generally has a lifespan of 30 years, although can last longer if the building is well maintained. There is a risk it can fail, particularly if it has been damaged by water ingress from leaking roofs which causes corrosion of the reinforcement, excessive thermal degradation, or if it was not formed correctly when originally made.  Poor original installation, cutting the reinforcement bars on-site, can dramatically reduce the end bearing capacity of the planks. It can fail suddenly, hence the recent action by the UK Government. Later RAAC planks are known to use galvanised steel or stainless steel reinforcing bars, and are of less concern provided the roof is kept watertight.

Concerns about RAAC are solely linked to its durability and structural performance, and there is no evidence to suggest that it poses any other health and safety risk. However, it is important to recognise that some earlier buildings incorporating RAAC are likely to contain ‘asbestos-containing materials’ in ceiling voids.  



RAAC panels are light-grey or white in appearance, the underside of the panels will appear smooth. The inside of the planks will appear bubbly, often described as looking like an Aero bar. Unlike traditional concrete, there will not be visible aggregate in the panels. Also, RAAC is very soft and easily penetrated.


RAAC panels are typically 600mm wide although this has been known to vary. Their length will vary, typically up to 6 metres. RAAC panels typically have a chamfer along their edge meaning there is a distinctive V-shaped groove every 600mm in the surface of the roof, floor or wall.



Consultants should be aware of the potential risks associated with RAAC and, where appropriate, conduct enquiries as to whether RAAC has been identified and, if so, the nature and status of any remediation plan, brief details of which should be incorporated in the survey report.

In the case of doubt (on the part of the policyholder), a recommendation should be considered calling for an inspection by a suitably qualified and appropriately experienced professional, such as an RICS chartered building surveyor or chartered structural engineer, who is experienced with this type of construction.   Guidance concerning suitably qualified professionals is detailed on page 15 of the Department for Education Identification Guidance.  

Regarding the educational sector, Consultants (pre-survey) should refer to the GOV.UK (Department for Education) list of educational settings where RAAC has been confirmed, as far as it relates to state-funded schools, maintained nursery schools and further education colleges in England.



Detailed information relating to RAAC can be found, for example, in the following publications, all of which are freely available online:

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